Presently, standardization of an image coding scheme called High Efficiency Video Coding (HEVC) has been progressing under work by the Joint Collaboration Team-Video Coding (JCTVC), a joint standards group between the ITU-T and the ISO/IEC, with the aim of further improving the coding efficiency over H.264/AVC.
With older image coding schemes such as MPEG-2 or H.264/AVC, a coding process is executed in processing units called macroblocks. Macroblocks are blocks having a uniform size of 16×16 pixels. Conversely, with HEVC, a coding process is executed in processing units called coding units (CUs). CUs are blocks having a variable size, formed by recursively dividing a largest coding unit (LCU). The maximum available CU size is 64×64 pixels. The minimum available CU size is 8×8 pixels. As a result of implementing CUs having a variable size, with HEVC it is possible to adaptively adjust image quality and coding efficiency according to image content. The question of how deep to divide an LCU (that is, what size of CU to use) is typically determined on the basis of a comparison of costs affecting the coding efficiency.